1. Field of the Invention
This invention relates generally to new and improved apparatus and method for the thorough, non-invasive mixing of a flowing fluid stream and, more particularly, to such apparatus and method as are particularly adapted for use in automated analytical devices of the continuous-flow type.
2. Description of the Prior Art
A variety of non-invasive mixing apparatus and methods are known in the prior art. However, none of the same are operative to effect complete mixing of a flowing fluid stream in presently contemplated high-speed automated continuous-flow analytical systems, for example, as disclosed in pending application for U.S. Letters Pat. Ser. No. 57,541 filed July 11, 1979 and assigned to the assignee hereof. Such systems may require that thorough mixing, at reasonable flow rates and in conduits of reasonable inner diameter, of a blood serum sample and one or more appropriate reagents be effected within less than ten seconds following mixing of sample and reagent. Moreover, since the blood serum samples are passed as a continuous stream comprising successive sample segments separated by inert fluid segments, mixing of the reagent with such successive segments must be effected without adverse effect on the integrity and/or isolation of the successive sample segments, as would result from an invasive mixing device, such as a mechanical stirrer.
For example, a helical mixing coil, as disclosed in U.S. Pat. No. 2,933,293 issued Apr. 19, 1960 to Andres Ferrari and assigned to the assignee hereof, is representative of prior art structures used for mixing in continuous-flow analytical systems. Such mixing coil which is described as relying for mixing primarily upon differences in specific gravities of the liquids to be mixed and which, in any event, markedly limits the mixing effects of secondary flow due to the generally invariant direction of fluid flow in the respective coils of the helix, i.e., counterclockwise as seen in the patent FIG. 8 and the resulting constancy and generally invariant orientation of the secondary flow patterns relative to the coil conduit. Experimental efforts have been made to adapt such helical mixing coils to meet these more stringent mixing requirements, including decreasing the inner diameter of the helix tubing and/or increasing the pitch or tightness of helical winding, with unacceptable results. The increase in back pressure exerted by the flowing fluid stream as a result of such efforts results in unsatisfactory system operation.